Does anyone else use WD-40 for case cleaning? I have found it works wonders at getting rid of surface grime, but does not ruin the patina. It also gets rid of that whitish crud frequently left inside cases that have been polished. Fingerprints, label marks and unwanted pen markings also disapper when wiped over with a rag sprayed with WD-40. Carbon deposits left by firing on newly fired cases also come off easily with it. The first thing I do when I get a new case or inert round with loose bullet is clean the much off the inside of the case with WD-40.
WD-40 is also used, by some, to inert primers prior to shipping or sectioning, & as such should not be used on / with ammo you might care to shoot.
I would assert (as Pete has implied) that on its own, this is NOT a reliable way to inert a primer, particularly long term! WD-40 will dry out over time and the effect may become, at best, something of a retardant. As Falcon notes, it is a cleaner with some lubricating properties. It does work to remove some surface blemishes, but then so do some other fluids such as alcohol and acetone.